Ultra-sensitive refractive index sensing enabled by a dramatic ellipsometric phase change at the band edge in a...

Surface plasmon polaritons (SPPs) and Bloch surface waves (BSWs) have been widely utilized to design sensitive refractive index sensors. However, SPP- and BSW-based refractive index sensors require additional coupling component (prism) or coupling structure (grating or fiber), which increases the difficulty to observe ultra-sensitive refractive index sensing in experiments. Herein, we realize dramatic ellipsometric phase change at the band edges in an all-dielectric one-dimensional photonic crystal for oblique incidence. By virtue of the dramatic ellipsometric phase change at the long-wavelength band edge, we design an ultra-sensitive refractive index sensor at near-infrared wavelengths. The minimal resolution of the designed sensor reaches 9.28×10^-8 RIU. Compared with SPP- and BSW-based refractive index sensors, the designed ultra-sensitive refractive index sensor does not require any additional coupling component or coupling structure. Such ultra-sensitive refractive index sensor would possess applications in monitoring temperature, humidity, pressure, and concentration of biological analytes.